Subsequent Events - Additional Information (Details) - USD ($) $ / shares in Units, $ in Thousands		1 Months Ended	2 Months Ended	12 Months Ended
	Jan. 10, 2018	Jan. 31, 2018	Feb. 21, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Subsequent Event [Line Items]
Net proceeds from sale of common stock						$ 461,136
ATM Sales Agreement
Subsequent Event [Line Items]
Common stock shares sold				912,351	1,159,415
Net proceeds from sale of common stock				$ 67,600	$ 79,500
Common stock shares sold				912,351	1,159,415
Subsequent Event
Subsequent Event [Line Items]
Sale of PRV	$ 130,000
Subsequent Event | ATM Sales Agreement
Subsequent Event [Line Items]
Common stock shares sold			240,417
Net proceeds from sale of common stock			$ 11,800
Common stock shares sold			240,417
Subsequent Event | Underwritten Public Offering
Subsequent Event [Line Items]
Common stock shares sold		5,043,860
Net proceeds from sale of common stock		$ 271,000
Common stock shares sold		5,043,860
Shares purchased by underwriters		657,895
Public offering price		$ 57.00